SEND DIAGNOSTIC command DEVOFFL and UNITOFFL bits

Elliott, Robert (Server Storage) Elliott at hp.com
Wed Jun 3 09:46:07 PDT 2009


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
*
During discussion of Mark Evans' proposal 09-087r2 at the last CAP WG meeting
to improve the standardese wording for the SPC-4 SEND DIAGNOSTIC command's
DEVOFFL and UNITOFFL bits, I did a web search to see how implementations have
actually been interpreting them.  It appears that few are using these bits as
intended. 
Their original definition was: 
- DEVOFFL means the test is allowed to take the entire SCSI target device
offline
- UNITOFFL means the test is allowed to take the logical unit offline (but
not affect other logical units in the SCSI target device)
I think it might be best to redefine these bits as "vendor-specific" to
reflect their real usage. 
Some example real usages:
1. IBM TotalStorage LTI Ultrium Tape Drive SCSI Reference at
http://dlc.sun.com/pdf/CRCM2172/CRCM2172.pdf.  Page 107 says DevOfl and
UnitOfl (sic) are "any value allowed and ignored" 
2. Exabyte Mammoth-2 tape drive SCSI reference at
http://www.exabyte.com/support/online/documentation/drives/33087602.pdf?CFID=
2719195.  Page 201 shows these combinations: 
DevOffL UnitOffL 
0	0	  Code check 
0	1	  Code check 
1	0	  Buffer check 
1	1	  Tape operation check 
3. STEC ZeusIOPS FC SSD Product Manual at
http://www.memtech.com/downloads/zeus_mach_manuals/ZeusIOPS_3_5_Fibre_Channel
_Product_Manual.pdf. Page 63 shows these combinations: 
DevOffL  UnitOffL 
0	 1	   do long self test (< 90 sec) 
1	 0	   do short self test (< 2 sec) 
4. Quantum DLT 7000 Tape Drive Product Manual at
http://downloads.quantum.com/dlt7000/dlt7000productmanual.pdf.	Page 206 has
a table: 
DevOfL	UnitOfL 
0	0	Self-test 1 
0	1	Self-test 2 
1	0	Self-test 1 
1	1	Self-test 2 
5. http://en.wikipedia.org/wiki/SCSI_Send_Diagnostic_Command has the DevOfL
and UnitOfL descriptions backwards.
---
Rob Elliott, HP Industry Standard Server Storage
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